Sensors & Transducers (Feb 2013)
Surface Plasmon Resonance Biosensor
Abstract
Performed in this paper is numerical modeling of the angular dependence for light reflectivity R(F) in surface plasmon-polariton resonance (SPR) realized in Kretschmann geometry when studying the interface gold/suspension of spherical particles (cells) in the assumption that the dielectric permittivity of particles suspension is described by the theory of effective medium. It has been shown that availability of suspended particles in solution inevitably results in appearance of an intermediate layer with the ε gradient between gold surface and suspension bulk, as a result of which the SPR angle shifts to lower values. Near the critical angle, the first derivative dR/dF demonstrates a clearly pronounced peak, which allows determining the value for suspension bulk and the gradient in the intermediate layer. Obtained in our experiments were SPR curves for two suspensions of erythrocytes – the dense one (erythrocyte mass after centrifuging) and loose solution (whole blood). In the case of erythrocyte mass, fitting the experimental and calculated curves enabled us to quantitatively determine the bulk value for this erythrocyte mass (εb =1.96), thickness of the intermediate layer dm (300…400 nm) and gradient in the intermediate layer. On the contrary, the SPR curve for whole blood appeared to be close to that of pure plasma. This fact allows only estimation of the thickness dm~2000...3000 nm as well as minimum ε value in the intermediate layer, which is close to that of plasma (ε = 1.79). Also, discussed is the mechanism of influence of the cell shape near the gold surface on the SPR effect.
